The Japanese Patent Unexamined Application Publication 6-111757 (designated as Document 1 hereinbelow) describes a photomultiplier with N number of independent electron multiplying portions disposed around a center axis. The photomultiplier includes a hermetically sealed container having a symmetrical structure along the longitudinal axis. The photomultiplier has a photocathode formed on the inner surface of the hermetically sealed container and a first dynode. The first dynode divides photoelectrons emitted from the photocathode into the N number of electron multiplying portions in accordance with the position on the photocathode which emits the photoelectron.
The first dynode has a cup shape with a flat bottom and a side face that extends towards the photocathode. The first dynode has a symmetric axis which substantially coincides with the longitudinal axis of the hermetically sealed container. The electron multiplying portion consists of sheet-type electron multipliers. An electrode is provided near a center on the bottom of the first dynode, and is maintained at the substantially same potential as that of the photocathode.
The Japanese Patent Unexamined Application Publication 7-192686 (designated as Document 2 hereinbelow) describes a photomultiplier tube with at least two space segments. This photomultiplier tube has a hermetically sealed container with a photocathode being formed inside. The hermetically sealed container includes a portion corresponding to a focusing electrode for focusing photoelectrons emitted from the photocathode and another portion corresponding to a first dynode performing the initial multiplication of photoelectrons.
The portion corresponding to the focusing electrode is separated from the portion corresponding to the first dynode by a flat plate. The flat plate has holes corresponding to each segment. The hole has a grid. A center partitioning wall having a flat surface that includes the center axis of the hermetically sealed container is provided on the opposite side to the side of the flat plate facing the photocathode. A second and higher order input dynodes are provided in the vicinity of the opposite side to the side of the center partitioning wall that faces the photocathode. A transverse rod is positioned at the center of the hermetically sealed container that includes the center axis. And the rod is parallel and distant away from the flat plate. The transverse rod is insulated from the electrode and maintained at the potential that is identical or similar to that of the photocathode.
The Japanese Patent Unexamined Application Publication 8-306335 (designated as Document 3 hereinbelow) describes a multi-channel type electron multiplier tube. The electron multiplier tube is provided with sheet-like dynodes having control electrodes between dynode sheets to control the gain of specific channels.
This multi-channel electron multiplier tube is provided with a hermetically sealed container having a photocathode on the inner surface, and cross-shaped projections between each channel. These projections are maintained at the same potential as that of the photocathode.
The Japanese Patent Unexamined Application Publication 11-250853 (designated as Document 4 hereinbelow) describes a photomultiplier tube in which an electron convergence space is divided into a plurality of segments by a partition plate. The partition plate in this photomultiplier tube extends from a position near the photocathode formed on the inner surface of the hermetically sealed container to the surface that includes the center axis of the hermetically sealed container. The partition plates have the same potential as the photocathode. Each segment is provided with a plurality of dynodes for multiplying electrons.